A corresponding wall structure for combustion chambers and thrust nozzles of liquid-fueled rocket engines has been known from, e.g., DE-PS 17 51 691. The cooling channels are incorporated in the wall structure described there in a one-piece basic body made of a material having good thermal conductivity, preferably copper, so that the hot gas-side inner wall and the radial webs between the cooling channels are integrally connected and consist of the same material. A layer of the same material as the basic body is applied as a thin outer wall to the webs from the outside by electroplating. This layer also acts as an adhesive layer for the relatively thick-walled outer jacket/pressure jacket made of a high-strength material having poor thermal conductivity, preferably nickel, which is subsequently applied by electroplating. This outer jacket also absorbs essentially the loads arising from the internal pressure in the combustion chamber and the nozzle via the webs and the thin outer wall.
The following processes take place during the operation of such a wall structure: Hydrogen having a temperature of, e.g., 30 to 200 K flows through the cooling channels, and the load-bearing outer jacket assumes approximately this temperature and its diameter even shrinks. This effect is further reinforced by stratification effects in the cooling agent, whose temperature increases at the inner bottom of the channel, i.e., at the inner wall, but remains relatively low in the outer zones. The temperature of the inner wall, which is made thin to ensure good heat transmission to the cooling agent, increases under the thermal load of the combustion space or of the nozzle due to the hot combustion gases, seeks to expand, but it is prevented from doing so by the counterpressure of the cold, rigid outer wall via the webs. As a result, the material of the inner wall flows in the direction of the transition areas to the webs. The longer the combustion time, the more pronounced is this effect. It stops only when the thermally induced stresses have decreased to the limit of elasticity. Thus, the radial wall thickness of the inner wall, which is thin anyway, decreases further approximately in the middle between the webs.
In the case of cutoff of the engine, the combustion is first terminated in the combustion space for safety reasons by shutting off the oxygen supply, whereas the hydrogen flowing through the cooling channels still continues to flow briefly. The thin inner wall is immediately cooled intensely because of its low heat capacity, which now leads to a high tensile load in it. This may lead to cracking in the weakened middle zones of the inner wall in a relatively short time, at least after repeated start-ups and prolonged burn times, and this cracking acutely jeopardizes the function of the combustion chamber or the nozzle and may lead to their complete destruction.
The manufacture of a regeneratively cooled rocket combustion chamber by electroforming by means of an electroplating core is described in DE-PS 21 37 109. The cooling structure manufactured in this manner has a thin inner wall, a thick, stable outer wall, and a plurality of webs, which extend radially between the inner wall and the outer wall, divide the intermediate space into a corresponding number of cooling channels, and mechanically support the inner wall. To reduce the thermal stresses in the area of the inner wall/webs, there are slots which are open toward the hot gas side and extend through the inner wall and the centers of the webs into the area of the outer wall. The inner wall, which is thus divided into a plurality of narrow strips with open "expansion joints" between them, is thus able to expand and contract relatively freely, i.e., to adapt itself to the thermal conditions. However, it should be borne in mind that the hot gases can penetrate into the gaps at least temporarily, so that hot gases are admitted to each cooling channel from one of three sides (1.times.inner wall, 2.times.webs). This results in an--at least temporarily--increased thermal load of the cooling structure. The corner areas of the inner wall/web are especially critical in terms of design. Due to the known, small dimensions of the cooling channel cross sections (a few mm in height and width), it is practically impossible to select exactly constant wall thicknesses, corner radii, etc., here. Weak points are thus unintentionally "preprogrammed," along with the risk of burnout and even structural failure. To counteract this risk, the middle wall thickness must again be increased, or the accuracy of manufacture must be improved. It might be obvious that the advantage of this design, which was initially suspected, is extensively eliminated by the above-mentioned drawbacks.